Primary venous aneurysms are infrequently noted and rarely have clinical significance. An important exception, however, is an aneurysm of the popliteal vein that is known to be a source for pulmonary emboli. We present the case of a previously healthy 57-year-old man with recurrent episodes of occult pulmonary embolism. Initial diagnostic investigations were compatible with multiple pulmonary emboli, but no source was identified. Subsequently, an indium 111-labeled platelet scan confirmed a site of active thrombus formation in the right lower extremity above the knee. Magnetic resonance imaging defined a saccular aneurysm of the popliteal vein, which was confirmed by contrast venography. Thereafter, the patient had resection of the venous aneurysm and tangential venorrhaphy. After operation duplex scanning confirmed patency of the venous repair. This is the eleventh report in the English-language literature of pulmonary emboli suspected of having originated from a popliteal venous aneurysm.